In this work, the conductance behavior of tungsten trioxide based chemoresistive ozone sensors under ultra violet illumination was investigated. The tungsten trioxide sensitive layers were deposited on a SiO2/Si substrate by reactive radio frequency magnetron sputtering with several Argon / Oxygen ratios. The detection principle is based on a change in the conductance of the semiconductor oxides when ozone is present around the surface. We demonstrate the influence of Argon / Oxygen during the deposition of the sensitive layer, on ozone detection at 50°C under light illumination. The sensor shows good sensitivity to ozone, with a stable baseline, fast response and recovery time. These results are promising for the detection of ozone at low temperature.